169
WSG-1068 IGNITION SYSTEM
Electronic Engine Controls
Refer to Section 08 of this manual.
Cylinder Head Temperature Sensor (CHT
Sensor)
The cylinder head temperature (CHT) sensor is a
thermistor device in which resistance changes with
temperature. The electrical resistance of a thermistor
decreases as temperature increases, and increases as
temperature decreases. The varying resistance affects
the voltage drop across the sensor terminals and
provides electrical signals to the GCP corresponding to
temperature.
Thermistor-type sensors are considered passive
sensors. A passive sensor is connected to a voltage
divider network so that varying the resistance of the
passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series
with the sensor resistor determines the voltage signal at
the GCP. This voltage signal is equal to the reference
voltage minus the voltage drop across the fixed resistor.
The CHT sensor is installed in the aluminum cylinder
head and measures the metal temperature. The CHT
sensor communicates an overheating condition to the
GCP. The GCP would then initiate a cooling strategy
based on information from the CHT sensor. A cooling
system failure such as low coolant or coolant loss could
cause an overheating condition. As a result, damage to
major engine components could occur. Using a CHT
sensor and cooling strategy would prevent damage by
allowing air cooling of the engine and limp home
capability.
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